A stent is a medical device placed in the body when there is abnormal circulation of blood and body fluid. The stent is typically inserted into blood vessels for the expansion of blood vessels that have been narrowed by lesions, and functions to open the blood vessels. Further, it is used to expand the digestive organs narrowed by lesions in the digestive tract and to release biological fluids into another passageway in case of blockage in the digestive tract, in addition to blood vessels. Stents made of materials including shape-memory alloys or polymers are used for the digestive tract, however, the use of those metal stents is limited as they are expensive.
The use of stents made of polymers is expected to increase due to relatively low price. However, in the case of polymer stents having a short diameter due to lack of expansibility compared to metal stents, they cannot function as a stent for a long period of time as biological materials may easily adhere to the inside thereof. Accordingly, it is important to prevent the adhesion of biological materials inside the stent when polymer stents are used. The adhesion of biological materials may lead to the formation of a bio-film due to adsorption of fibers from the digestive organs by food, proteins of biological fluid, etc., thereby narrowing the stent, which is then unable to function. Accordingly, the adhesion of biological materials must be minimized in order for the stents to function and to be used for a long time.
A method for treating vascular diseases includes a technique that uses artificial blood vessels, in addition to the stents which are prosthetic medical devices. Vascular diseases are mainly caused by thickening of arteries due to fat accumulation, or plaque (or atheroma), leading to hardening of the arteries. The arteries supply blood, oxygen, and nutrients from the heart to all parts of the body. Therefore, the arteries that have become narrow and stiff may result in restricted blood flow and a decrease in supplying these materials to each organ. Such an inadequate supply of blood may lead to dysfunction, tissue damage, and even death in severe cases. Therefore, drugs that help relax arteries are administered in order to treat such vascular diseases, however, a treatment with drugs merely improves the symptoms. There is little cure for the vascular diseases, and thus it is inconvenient that patients need to take the drugs for life. Another treatment method includes surgery in which damaged vessels are removed and artificial vessels are transplanted to the affected site.
Although methods of transplanting arteries or veins of donors have been initially implemented, they suffer from low success rates due to rejection or sclerosis. Hence, research and development into synthetic (artificial) blood vessels has been conducted. Artificial blood vessels for transplantation must be made of materials which are harmless to the human body and have high biocompatibility. Furthermore, these materials should not be rejected by the immune system and should be maintainable in vivo for a long time. Also, there should be no case in which blood vessels are clogged by precipitation of proteins or lipids or due to thrombosis.
As such, polymer materials are being used as biomaterials which can be used for stents, artificial blood vessels, etc., due to high biostability. As described above, it is important that the inside and outside of a transplant be uniformly modified to have appropriate features in order to prevent side effects by inhibiting precipitation of proteins or lipids, or thrombosis, and to improve an engraftment of the transplant by improving cell adhesion. However, polymers are typical insulators, which have low permittivity, and therefore plasma can hardly be generated, thereby imposing limitations on a surface treatment by plasma. Specifically, surface modifications with uniformity cannot be easily achieved by a common surface treatment method in the case of an inner wall of a tube having a small internal diameter, such as small-diameter stents or artificial blood vessels, or an artificial organ having an irregular shape, such as an artificial heart.